The present invention relates to a liquid crystal display device, and in particular to a liquid crystal display device provided with a gate driver compatible with both the so-called Cs-on-common structure and the so-called Cs-on-gate structure.
Conventionally, liquid crystal display devices using the active matrix driving method, provided with TFT (thin-film transistor) elements as switching elements for selective driving of pixel electrodes, are known (see Japanese Unexamined Patent Publication Nos. 3-177890/1991 (Tokukaihei 3-177890, published on Aug. 1, 1991) and 10-274783/1998 (Tokukaihei 10-274783, published on Oct. 13, 1998). Structures for a liquid crystal panel provided in such a liquid crystal display device include the so-called Cs-on-common and Cs-on-gate structures.
As shown in FIG. 15, a liquid crystal display device 101 provided with a liquid crystal panel 102 having a Cs-on-common structure includes a gate driver 103, a source driver 104, a control circuit 105, a power circuit 106 which is a power source for the liquid crystal driving system, and a counter electrode driving circuit 107. The liquid crystal panel 102 includes a plurality of gate electrode lines 108 and source electrode lines 109, extending in intersecting directions on an insulating substrate, and is driven by the active matrix driving method. In the vicinity of the areas where the respective gate and source signal lines 108 and 109 cross, the liquid crystal panel 102 is provided with pixel electrodes, TFT elements, liquid crystal capacitances, auxiliary capacitances, etc., which are structures necessary for display operations. Auxiliary capacitance electrodes are connected to a capacitance line (connected in turn to a counter electrode line connected to the counter electrode), and are all fixed at a common potential.
The counter electrode driving circuit 107 supplies a counter electrode signal AC to the counter electrode of the liquid crystal panel 102 and, via the capacitance line, to the auxiliary capacitance electrodes. The power circuit 106 applies a plurality of voltages (to be discussed below) to the gate and source drivers 103 and 104. The control circuit 105 supplies various signals, such as a clock signal CK and a start pulse signal SP, to the gate and source drivers 103 and 104.
The operations of the gate driver 103 are controlled based on the signals supplied by the control circuit 105, such as the clock signal CK and the start pulse signal SP. The plurality of voltages from the power circuit 106 are applied to the gate driver 103, which supplies signals to the plurality of gate signal lines 108.
The operations of the source driver 104 are controlled based on the signals supplied by the control circuit 105. The plurality of voltages from the power circuit 106 are applied to the source driver 104, which supplies signals to the plurality of source signal lines 109. The source driver 104 drives the pixel electrodes of the liquid crystal panel by applying voltages to the source signal lines 109.
As shown in FIG. 16, the gate driver 103 is made up of a control logic 111, a bi-directional shift register 112, a level shifter 113, an output circuit 114, etc. The gate driver 103 is also provided with terminals for accepting input of the clock signal CK, the start pulse signal SP, a voltage VCC (power source voltage), a voltage GND (ground voltage), and a voltage VDD, and is provided with a plurality of output terminals OS1 through OSn.
The control logic 111 generates and supplies to the bi-directional shift register 112 a signal necessary for the operation thereof. The bidirectional shift register 112, upon receipt of the clock signal CK and the start pulse signal SP, performs shift operations to successively synchronize the start pulse signal SP with the clock signal CK. The bi-directional shift register 112 generates and outputs to the level shifter 113 selection pulses for selecting which pixel electrodes of the liquid crystal panel 102 are to be driven by application of voltage to the source signal lines 109 by the source driver 104. The level shifter 113 converts the voltage of each selection pulse to a level required for ON/OFF (selection/non-selection) operation of the TFT elements of the liquid crystal panel 102, and outputs the converted voltages to the output circuit 114.
The output circuit 114, based on the signals received from the level shifter 113, applies voltages of levels necessary for ON/OFF operation of the TFT elements to the gate signal lines 108 via the corresponding output terminals OS1 through OSn. In other words, as shown in FIG. 17, when an input signal of voltage VCC is supplied, the output circuit 114 supplies an output signal of voltage VDD successively to the output terminals OS1 through OSn, but when no input signal is supplied (when voltage is GND), the output circuit 114 supplies an output signal of voltage VSS to the output terminals OS1 through OSn.
In contrast, a liquid crystal display device 121 provided with a liquid crystal panel 122 having a Cs-on-gate structure, shown in FIG. 18, includes a gate driver 123 instead of the gate driver 103. Each auxiliary capacitance electrode of the liquid crystal panel 122 is connected to an adjacent gate signal line 108. In other words, the gate signal lines 108 are also used as capacitance lines, and each electrode receives superimposed signals.
The counter electrode driving circuit 107 supplies the counter electrode signal AC to both the power circuit 106 and the counter electrode of the liquid crystal panel 122. The power circuit 106, based on the counter electrode signal AC supplied from the counter electrode driving circuit 107, generates a rectangular wave signal ACK and supplies it to the gate driver 123.
As shown in FIG. 19, the gate driver 123 further includes an input terminal for receiving input of the rectangular wave signal ACK. The rectangular wave signal ACK is supplied to the output circuit 114. The output circuit 114, based on the signal received from the level shifter 113 and the rectangular wave signal ACK, applies voltages of levels necessary for ON/OFF operation of the TFT elements to the gate signal lines 108 via the corresponding output terminals OS1 through OSn. In other words, as shown in FIG. 20, when an input signal of voltage VCC is supplied, the output circuit 114 supplies an output signal of voltage VDD successively to the output terminals OS1 through OSn, but when no input signal is supplied (when voltage is GND), the output circuit 114 supplies the rectangular wave signal ACK to the output terminals OS1 through OSn.
As explained above, the power circuit and the gate driver for driving the gate signal lines are structured differently in a liquid crystal display device provided with a liquid crystal panel having the Cs-on-common structure and one provided with a liquid crystal panel having the Cs-on-gate structure. In other words, since liquid crystal panels of the Cs-on-common and Cs-on-gate structures use different respective methods to drive the gate signal lines, in the foregoing conventional liquid crystal display devices, it was necessary to use (install in the liquid crystal display device) one of two different types of gate driver and power circuit, depending on the structure of the liquid crystal panel. Accordingly, shortcomings of the conventional art were that the process for manufacturing liquid crystal display devices was complicated, and the liquid crystal display devices manufactured thereby were not versatile.
It is an object of the present invention to provide a liquid crystal display device able to drive gate signal lines of display means of both the so-called Cs-on-common structure and the so-called Cs-on-gate structure, using a single driving means and a single power source device.
In order to attain the foregoing object, a liquid crystal display device according to the present invention is made up of driving means capable of driving gate signal lines of display means having a first structure, in which auxiliary capacitance electrodes forming auxiliary capacitances with pixel electrodes are connected to capacitance lines, and capable of driving gate signal lines of display means having a second structure, in which the auxiliary capacitance electrodes are connected to the gate signal lines; and a power source device which applies a voltage to the display means through the driving means; in which the driving means include switching means for changing the voltage applied to the display means from the power source device, to enable driving of the gate signal lines in accordance with the first or second structure of the display means.
With the foregoing structure, the driving means for driving the gate signal lines include switching means, which change the voltage applied to the display means from the power source device in accordance with the structure of the display means. In-this way, by providing the driving means with switching means which change the voltage applied from the power source device so as to be compatible with both the Cs-on-common and Cs-on-gate structures, the liquid crystal display device according to the present invention can perform gate signal line driving which is in accordance with the structure of the display means, using a single driving means. Consequently, it is not necessary to provide the liquid crystal display device with two kinds of driving means and switch back and forth between them depending on the structure of the display means. Accordingly, the process for manufacturing the liquid crystal display device can be simplified, and versatility of the liquid crystal display device can be improved.
Further, the liquid crystal display device according to the present invention is preferably structured as above, further provided with voltage generating means for generating a voltage for AC driving of gate signal lines of display means having the second structure, in which the auxiliary capacitance electrodes are connected to the gate signal lines.
In this way, by providing, for example, the power source device or the switching means with voltage generating means for generating a voltage for AC driving of gate signal lines of display means of the Cs-on-gate structure, the liquid crystal display device according to the present invention can apply voltages and perform gate signal line driving which is in accordance with the structure of the display means, using a single driving means. Consequently, it is not necessary to provide the liquid crystal display device with two kinds of driving means and switch back and forth between them depending on the structure of the display means. Accordingly, the process for manufacturing the liquid crystal display device can be simplified, and versatility of the liquid crystal display device can be improved.
Moreover, when the foregoing voltage generating means are provided in the switching means, the power source device, which is a so-called peripheral device (circuit), can be streamlined, thus contributing to miniaturization of the liquid crystal display device in cases when portability of the liquid crystal display device is highly desirable.
Further, the liquid crystal display device according to the present invention is preferably structured as above, further provided with power consumption reducing means for stopping operation of the voltage generating means during stand-by of the liquid crystal display device.
By providing the liquid crystal display device according to the present invention with power consumption reducing means, operation of the voltage generating means can be stopped during stand-by. Accordingly, the power consumed by operation of the voltage generating means can be saved, thus reducing the power consumption of the liquid crystal display device during stand-by.
Additional objects, features, and strengths of the present invention will be made clear by the description below. Further, the advantages of the present invention will be evident from the following explanation in reference to the drawings.